盾构隧道穿越上软下硬地层地表变形数值模拟研究

盾构隧道在上软下硬地层掘进时，由于掌子面地层物理力学性质复杂，易引起地面沉降或隆起。文章以芜湖城南过江隧道为工程背景，探讨隧道穿越上软下硬地层时地表变形规律。运用FLAC3D软件对典型上软下硬地层区间施工过程进行数值模拟，结合现场监测数据，分析隧道埋深、掌子面砂层与岩层厚度比、掌子面附加压力对地表变形影响。结果表明：砂层中地表沉降与隧道埋深呈正相关；复合地层中地表沉降与开挖面砂层厚度占比呈正相关；开挖面附加压力存在最适区间，超过最适区间都会引起地层变形增大。该研究结果可为上软下硬地层中隧道施工提供指导。

When the shield tunnel passes through the upper soft and lower hard strata, it is easier to cause the ground subsidence or uplift because of the complex physical and mechanical properties of the strata on the palm face. In this paper, the Wuhu Chengnan River Crossing Tunnel is taken as the engineering background to explore the law of the ground surface deformation when the tunnel crosses the upper soft and lower hard strata. The FLAC3D is used to simulate the construction process of typical upper soft and lower hard strata, and the influence of tunnel burial depth, thickness ratio of sand layer to rock layer and additional pressure at the palm face on the ground surface deformation is analyzed. The conclusions are as follows: the ground surface settlement in the sand layer is positively correlated with the tunnel burial depth, the ground surface settlement in the composite strata is positively correlated with the proportion of sand layer thickness at the palm face, and there is an optimum interval of the additional pressure at the palm face, exceeding the optimum interval will cause increased strata deformation. This research has guiding significance for the construction of tunnels in upper soft and lower hard strata.